Add a fast-path for independent inherited properties

third_party/WebKit/Source/core/dom/Element.cpp

Index: third_party/WebKit/Source/core/dom/Element.cpp
diff --git a/third_party/WebKit/Source/core/dom/Element.cpp b/third_party/WebKit/Source/core/dom/Element.cpp
index 67e29c95e205616ad139015f196de9e2d76be911..8941173e1e8606d1a9b31d03bd2d40299f39762d 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -1703,12 +1703,13 @@ void Element::recalcStyle(StyleRecalcChange change, Text* nextTextSibling)
     if (hasCustomStyleCallbacks())
         willRecalcStyle(change);
 
-    if (change >= Inherit || needsStyleRecalc()) {
+    if (change >= IndependentInherit || needsStyleRecalc()) {
         if (hasRareData()) {
             ElementRareData* data = elementRareData();
-            data->clearComputedStyle();
+            if (change != IndependentInherit)
+                data->clearComputedStyle();
 
-            if (change >= Inherit) {
+            if (change >= IndependentInherit) {
                 if (ElementAnimations* elementAnimations = data->elementAnimations())
                     elementAnimations->setAnimationStyleChange(false);
             }
@@ -1752,15 +1753,37 @@ void Element::recalcStyle(StyleRecalcChange change, Text* nextTextSibling)
         reattachWhitespaceSiblingsIfNeeded(nextTextSibling);
 }
 
+bool Element::canPropagateInheritedProperties(StyleRecalcChange change)
+{
+    return change == IndependentInherit
+        && !needsStyleRecalc()
+        && computedStyle()
+        && parentComputedStyle()
+        && !computedStyle()->animations()
+        && !computedStyle()->transitions()
+        && !hasAnimations();
+}
+
 StyleRecalcChange Element::recalcOwnStyle(StyleRecalcChange change)
 {
     DCHECK(document().inStyleRecalc());
     DCHECK(!parentOrShadowHostNode()->needsStyleRecalc());
-    DCHECK(change >= Inherit || needsStyleRecalc());
+    DCHECK(change >= IndependentInherit || needsStyleRecalc());
     DCHECK(parentComputedStyle());
 
     RefPtr<ComputedStyle> oldStyle = mutableComputedStyle();
-    RefPtr<ComputedStyle> newStyle = styleForLayoutObject();
+    RefPtr<ComputedStyle> newStyle;
+
+    // When propagating inherited changes, we don't need to do a full style recalc
+    // if the only changed properties are independent. In this case, we can simply
+    // set these directly on the ComputedStyle object.
+    if (canPropagateInheritedProperties(change)) {
+        newStyle = ComputedStyle::clone(*computedStyle());
+        ComputedStyle::propagateIndependentInheritedProperties(*parentComputedStyle(), *newStyle);
+        INCREMENT_STYLE_STATS_COUNTER(document().styleEngine(), independentInheritedStylesPropagated, 1);
+    } else {
+        newStyle = styleForLayoutObject();
+    }
     DCHECK(newStyle);
 
     StyleRecalcChange localChange = ComputedStyle::stylePropagationDiff(oldStyle.get(), newStyle.get());
@@ -1800,7 +1823,7 @@ StyleRecalcChange Element::recalcOwnStyle(StyleRecalcChange change)
     if (change > Inherit || localChange > Inherit)
         return max(localChange, change);
 
-    if (localChange < Inherit) {
+    if (localChange < IndependentInherit) {
         if (oldStyle->hasChildDependentFlags()) {
             if (childNeedsStyleRecalc())
                 return Inherit;